Brake caliper grooves

[Gearhead]

87 VR, lots of miles. I figured I'd post this in General Tech because I bet the calipers are about the same.

 

I had noticed that my rear pads were worn thin at the aft end, but much thicker at the forward end. It had me wondering if the forward pistons were seized, but they are not. Then I noticed significant grooves, maybe 1/32" deep, in the forward surface of the brake-pad-cavity in the caliper. The braking forces shove the pads forward against these surfaces whenever the rear brakes are used, and the backing plates have worn these grooves. They then get caught in the grooves, not allowing the pads to clamp any closer to the rotors at the forward edge, causing the wedge-shaped wear on the pads. Make sense?

 

Anybody else seen this? I thought about filing the surrounding material down to make it smooth again, but then the cavity will be bigger than it's supposed to be and the pads might not contact that surface like they are supposed to. But I don't know that I have any choice, short of replacing the caliper.

 

Ideas?

 

Thanks, Jeremy

[skydoc_17]

Hey Jeremy,

You are correct! If you take a closer look at the two pin holes that hold the brake pad backing plates, you will find that they are elongated. (egg shaped) The MKII rotor diameter is so large, and the surface footage that the rear caliper is exposed to is so great that the Aluminum material the caliper body is made from can't handle the braking force. So to answer your question, yes I have seen this many times, it is the pins elongating that causes the pads to "cock", and cut the groves in the clearance area of the caliper body. If your caliper is in this condition, then it needs to be replaced.

On a side note, I have a 4 piston, progressive engagement, (two different piston sizes) rear caliper from an FJR1300 that has been completely rebuilt, loaded with brand new EBC HH Sintered brake pads, if you are interested, feel free to PM me.

If you do decide to replace that caliper from a place like Ebay, (where you can't physically lay your hands on the caliper) Request pics of the area where the rotor rides inside the caliper. If you don't, you will have TWO calipers in the same condition!

I have 25 or so of them here at the shop.

Earl

[Gearhead]

Hey Earl, I thought I'd bring this back to the forum so others can benefit.

 

I checked the caliper out and sure enough, the pin holes are egged. Not as severely as I thought they might be, though. It doesn't take much. The pins are also worn from .185" in the "non-wear" areas down to .180".

 

I checked my fronts and actually they have a bit of the problem, though not as severe. You said in a PM that the left front caliper has smaller pistons than the right front - is this to give the right front greater stopping power with the hand brake alone?

 

So the FJR caliper is a bolt-on solution and can be used with the linked brake system?

 

Finally, because I have 3 calipers in some stage of this condition, I am thinking more about drilling out the pin holes and installing bronze bushings. I can get bushings that are 3/16 ID (just right for the pins) x 1/4 OD, drill out the holes on a drill press, light press the bushings in and stake them in place on both ends. I'm going to check in to new pins also.

 

Jeremy

[SPORTZAGE]

Earl,

I'd also like to know if the calipers are a simple plug and play to the existing system. What year bikes will they fit. And what kinda money we talking to get a rear caliper? I haven't even checked mine yet but I've noticed lately a severe loss in rear (pedal) braking so I'm gonna guess I better ask now and look soon... Replaced the left front pads recently and had really good braking for a short time.

Bob

[Gearhead]

Hey Bob, I bet you do have this going on. Does your pedal seem low, and does pumping help? That's been the case with mine and I thought I could never get it bled right. But now I'm thinking that with the rear AND the left front grooved such that the pads were hanging up on one end, that was causing the need to pump the brake. Theory: when your pads were new, they were nice and thick and lined up with the caliper grooves so it wasn't a problem. When they started to wear, the grooves started holding them off the rotor.

 

Jeremy

[SPORTZAGE]

Jeremy,

Yep pedal seems to be dropping lower and lower and I find myself pumping altho I'm not sure it really helps. They will eventually work but you have to really be pushing hard if you are in any kind of hurry to stop. Poor ole bike. I sure wish they would go back and make this one again but yeah I know...If a frog had wings...LOL. I'll take a look next day off.

[Gearhead]

Hey Y'all,

 

A while back I had the problem documented here with my brakes. I fixed them as follows: I bought bushings that are 3/16 ID (just right for the pins) x 1/4 OD, drilled out the holes on a drill press and light pressed the bushings in. I also bought new pins, 3/16 dia. All hardware came from McMaster Carr and cost just a few bucks. I also filed down the surface with the grooves until the grooves were essentially gone.

 

I have attached pretty detailed pics. They aren't great, phone camera, but they get the point across. In the "wear_grooves" pic, the grooves are near and in the part that looks blue. The "egg_holes" pic is supposed to show the egg-shaped holes before I did anything, but it's pretty hard to see. The file names of the pics are fairly descriptive.

 

The process took me a while, but saved getting at least two and maybe 3 new calipers.

 

Jeremy